In the art to which this invention relates it has been customary to hold the jaw of the fifth wheel into contact with the king pin by means of a slidable wedge. The wedge was held in place between a part of the frame of the fifth wheel and the off-king pin side of the jaw. Means is provided to unlock the mechanism by first moving the wedge to a retracted position followed shortly thereafter by movement of the jaw, permitting the king pin to be removed from the fifth wheel.
In some instances it has been found that the wedge was jammed so tightly in place that it was impossible to remove the same by means of the usual handle associated therewith. Further, in prior apparatus it has been necessary to limit the inward movement of the wedge so that in the event the king pin became oval shaped in the fore and aft direction of normal movement of the vehicle, there would be no overstressing of the parts when the tractor turned at substantially right angles to the trailer. In other words, when a king pin becomes worn it wears somewhat oval shaped in the fore and aft, normal towing direction of the vehicle. If the wedge continues to be forced inwardly, when it is permitted to move inwardly, thus to move the jaw closer to the king pin, then, when the tractor is maneuvered so as to be substantially at right angles to the trailer, as when parking for unloading, etc., excessive force is placed upon the parts, causing undue stress on the several parts including the king pin, jaw and wedge and associated frame parts.
The state of the art can be traced from my father's U.S. Pat. No. 2,371,750, through my U.S. Pat. Nos. 3,318,616, 3,844,854, 3,630,545, and most recently, in my U.S. Pat. No. 4,140,328. In the '328 patent, means is disclosed to provide access from the exterior of the fifth wheel for freeing a jammed or stuck wedge. A rod like member is mounted for sliding movements in the depending or vertically disposed portions of the frame of the fifth wheel. The member is threaded for a length adjacent its outer end and a spring is interposed between two of the depending frame members. A nut is provided adjacent the spring so that the location of the inner end of the member relative to the end of the wedge may be adjusted. By simply striking the projecting outer end of the member, the entire member moves inwardly, thus freeing the jammed wedge from the exterior or outside of the fifth wheel.
The current state of the art using a jaw and wedge has a handle that has slots which contact studs in the jaw and wedge. The slot for the wedge allows approximately one and one-half inches of motion when the handle is secure in a locked position and has a tendency to squirt when grease and dirt get between the contacting surfaces of the jaw and wedge. This action can cause the wedge to strike the handle with force towards the open position.